Accurate determinations of sensor pose (i.e., sensor position and attitude) provide essential information for passive ranging methods in sensor systems using this type of range measurement technique. Passive ranging has important practical applications in covert terrain-following and terrain-avoidance methods and in certain missile systems uses. For example, sensors that track objects and images, such as those sensors that fire-and-forget missiles possess, require accurate estimates of sensor pose during target intercept and other operations where the missile sensor moves relative to a tracked object.
To determine the sensor pose, it is necessary to accurately determine the sensor attitude. Attitude determination, however, is an ill-conditioned problem. Most tracking sensors employ image correlation and comparison methods based on local statical distributions of pixel intensity for attitude determinations. For example, adaptive gate centroid trackers use a template to correlate images that the sensor systems keeps as a "reference" in memory for this purpose.
These and other methods for accurately determining sensor pose are important for passive ranging algorithms. Passive ranging algorithms, however, are sensitive to errors that exist during range calculations. Errors in passive range calculations are in large part the result of two factors. The first factor is small errors that exist in correlating the sensed image to the reference image in the memory. The second factor is small error resulting from a decoupling that occurs between the sensor and the navigation system (e.g., an INS system) as the aircraft structure or platform containing the sensor flexes or changes shape.
Present sensor systems that perform passive ranging do not address the ill-conditioning that exists in the attitude determination problem. Thus, there is a need for a method that provides accurate attitude determination for the purpose of calculating sensor pose during passive ranging.
There is a need for a method to determine sensor attitude that overcomes the decoupling between the sensor and the navigation system that occurs as a result of aircraft or platform flexture.
Moreover, there is a need for a method and system that minimizes the effect of calculation errors that may exist during the correlation of a template or other reference in memory to the sensed image that the sensor detects.